The present invention relates to signals, in particular, Light Emitting Diode (LED) Signals. More specifically, the present invention relates to an LED traffic signal that is less susceptible to the xe2x80x9csun phantomxe2x80x9d effect, having an improved viewing aspect, as well as materials, manufacturing and installation cost advantages.
LED traffic signals present numerous advantages over common incandescent lamp traffic signals. Use of LED""s provides a power consumption savings and extremely long life in comparison to common incandescent light sources. The long life span creates improved reliability and sharply lowered maintenance costs.
As an individual LED is not bright enough to equal the light output of an incandescent lamp, multiple LED""s are used. Previously, multiple LED""s created a display aspect with multiple individual points of light readily discernible by the viewer. A non-uniform display aspect is commercially undesirable for traffic signals. One method of preventing discernable individual light points has been to use a full array of LED""s. However this is not commercially competitive as each additional LED is a significant percentage of the signals total cost. Each generation of LED""s is becoming brighter and brighter requiring fewer and fewer LEDs to equal the light output of an incandescent lamp but at the same time increasing the likelihood that the individual point sources and/or shadows between each LED are then detectable by the viewer.
Due to the large installed base, worldwide, of incandescent traffic signal systems, most LED traffic signals are designed to be retrofitted into existing traffic signal systems originally designed for incandescent lamps. To allow an easy retrofit to an LED light source, without requiring large changes to existing intersection alternating, current power distribution and logic circuits, signal assemblies incorporate a power supply to d rive LED""s at a lower, controlled, direct current power level. In the past, this has resulted in an LED traffic signal assembly with a separate power supply built on a Printed Circuit Board (PCB) and a separate LED matrix PCB connected via wiring between the two PCB""s as well as spliced into the original incandescent power wiring. Integration of LEDs onto a single PCB including the power supply results in a smaller PCB with corresponding manufacturing and cost of materials benefits.
Cost of materials and assembly time contribute to total cost and therefore to commercial success. Previous LED traffic signals used a large number of total components, each individual component adding material cost, assembly cost and introducing a potential quality control, moisture, and/or vibration failure opportunity.
Traffic signals are susceptible to xe2x80x9csun phantomxe2x80x9d phenomena. When a light source, for example the sun, shines upon the face of a traffic signal, a bright spot, or worse, internal reflection from within the signal, may make it appear to a viewer that the signal is energized when, in fact, it is not, leading to an increased chance for accidents.
Previous incandescent signals have attempted to prevent the xe2x80x9csun phantomxe2x80x9d phenomena by using a visor, internal or external baffles and/or a flat outer face angled towards the ground. Visor""s and external baffles limit the viewing angle of the signal. Internal baffles add cost to the signal by introducing an element that has no other purpose. Flat outer faces are not allowed, according to some traffic signal specifications which require a spherical front element.
Previous LED signal lamps are especially susceptible to xe2x80x9csun phantomxe2x80x9d phenomena because the rear surface of each LED is highly reflective. Previous LED signal designs located the LED""s on or close to the outer surface where the rear surface of each LED could easily be reached by stray light, creating an increased opportunity for xe2x80x9csun phantomxe2x80x9d reflections.
Therefore, the present invention has the following objectives:
1. An LED signal which minimizes the problem of xe2x80x9csun phantomxe2x80x9d erroneous signal aspects.
2. An LED signal which presents a uniform brightness display aspect equal to or better than a common incandescent lamp traffic signal.
3. An LED signal that has materials and manufacturing assembly cost advantages.
4. An LED signal comprised of a single printed circuit board carrying both the LED""s and the power supply components.
5. An LED signal retro-fitable Into existing incandescent traffic signals, without requiring removal of the existing reflector assembly.
6. An LED signal capable of easy upgrade to higher output LEDs without requiring recalculation of the optical elements.
7. An LED signal with a display aspect unaffected by changes in individual LED light output.
8. An LED signal usable in multiple configurations, each specific to a given application, with a minimum of unique components being required.
Further objects will be realized by one skilled in the art, through review of the following description and appended claims.
The above objects and other advantages are achieved with the present invention. Placement of the LEDs, to create an overlapping light emission pattern at an increased distance from a Multiple Collimating Zone Element (MCZE) creates a uniform display aspect for the signal, without individual points of light. The increased distance also allows placement of power supply components and circuitry on a single PCB with the LEDs, spaced so as to prevent interference with the LED light. The xe2x80x9csun phantomxe2x80x9d phenomena is prevented by a large radius spherical outer distribution cover, angled to reflect stray light away from the viewer, towards the ground. A complex inner surface on the distribution cover creates a shaped light distribution, focused upon the viewer, while at the same time further directing stray light reflections, again, towards the ground. Materials, assembly and installation cost efficiencies are realized by a novel snap together housing design which adds to an overall reduction in total number of components. The signal fits into existing standard incandescent traffic signals upon removal only of the incandescent bulb and original outer lens. Electrical connection is made by merely screwing a socket mating connector into the existing incandescent socket.